Add an option to pass a truststore in a format of a base64 string

[M0arcin]

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Feature description

The current implementation of passing TrustStore is limited to a path to certain storage - either hdfs or some other location elasticsearch-hadoop could access. It burdens the user with uploading and maintaining the file somewhere, which can be quite a challenge in the case of many connections.

To simplify the process, Truststore could be loaded from a base64 string, decrypted, and loaded inside the elasticsearch-hadoop package. Of course, such functionality could be allowed on top of the existing solution as an additional parameter.

[M0arcin]

PR @ #2027
Not sure why it wasn't connected